Why no breaker used in Bus Potential Transformer feeder???

[VINODH]

http://www.crazyengineers.com/community/threads/bus-pt-feeder.51778/

Kindly go through this discussion and help me with the vital reason. Thank you.

 

[Smart $]

http://www.crazyengineers.com/community/threads/bus-pt-feeder.51778/

Kindly go through this discussion and help me with the vital reason. Thank you.

Broken english descriptions leave much desired. Hard to say without seeing the diagram(s). I'm not going to join just to see them.

 

[VINODH]

Bus Pt feeder

Bus Pt feeder

Sorry for unclear attachment.
Hereby I hav attached clear view of 11kV Bus Potential Transformer feeder.
Initially, I will share on wat i understood from the drawing. Please correct me if am wrong.
As per the drawing, I feel just an MCB is enough for protection rather than using a breaker.Incoming supply 11kV and output is 110V with fuses connected to metering and Protection Cores. Once the relay acts on undervolt or no volt, relay just opens CB and protects PT.

Please come out with your replies.

 

[rcwilson]

Your one line shows Molded Case Circuit Breakers (MCB) protecting the 110V secondary and an 11 kV fuse for clearing a faulted voltage transformer (VT). That is normal design for medimum voltage (15 kV Class) switchgear.

I don't understand your comment about the undervoltage tripping a breaker to protect the VT. If a VT has a problem, it is destroyed. There is no fuse or relay you can put on the circuit to clear the fault before the VT is destroyed. The fuse is there to prevent the fault from escalating and to isolate the fault from the system.

A fuse and VT disconnecting drawer assembly is about $2,500 including VT and fuses. An 11 kV breaker is about $25,000 not including the required CT's and protection relays. An 11 kV breaker will not be able to trip in time to save a VT since it is inherently slower than a fuse.

If you want to spend 10 times more money and 4 times the space to protect a potential transformer, you could. But engineers designing switchgear for the last 80 years haven't seen a need to do it.

 

[VINODH]

Your one line shows Molded Case Circuit Breakers (MCB) protecting the 110V secondary and an 11 kV fuse for clearing a faulted voltage transformer (VT). That is normal design for medimum voltage (15 kV Class) switchgear.

I don't understand your comment about the undervoltage tripping a breaker to protect the VT. If a VT has a problem, it is destroyed. There is no fuse or relay you can put on the circuit to clear the fault before the VT is destroyed. The fuse is there to prevent the fault from escalating and to isolate the fault from the system.

A fuse and VT disconnecting drawer assembly is about $2,500 including VT and fuses. An 11 kV breaker is about $25,000 not including the required CT's and protection relays. An 11 kV breaker will not be able to trip in time to save a VT since it is inherently slower than a fuse.

If you want to spend 10 times more money and 4 times the space to protect a potential transformer, you could. But engineers designing switchgear for the last 80 years haven't seen a need to do it.

thanks a lot Sir!!!!Most of them i enquired about this cant give a clear explanation as u did now.
i meant in the same way as u told ...might be my words of expressing would have been wrong...

 

[zog]

Might be....

 

[T.M.Haja Sahib]

Vinodh:
If the VT you are talking about is oil filled,you may need better protection such as a current limiting H.V fuse on the primary side of VT to prevent explosion due to any arcing fault inside the VT.You may check up with the concerned manufacturer on this point.

 

[VINODH]

bus Pt feeder

bus Pt feeder

Vinodh:
If the VT you are talking about is oil filled,you may need better protection such as a current limiting H.V fuse on the primary side of VT to prevent explosion due to any arcing fault inside the VT.You may check up with the concerned manufacturer on this point.

Yes sir, Thank you.As you pointed out, its oil filled VT only.Sure I will go through manufacturers manual for additional information.

 

[T.M.Haja Sahib]

I think using current limiting fuse instead ordinary HRC fuse for VT primary protection is relatively a new concept.So it is fruitful,if you have a discussion with the manufacturer directly.